Some internal combustion engines utilize boosting devices such as turbochargers to increase the mass airflow through the engine, thereby enabling an increase of the work output of the engine. As one example, an engine may utilize twin turbochargers in separate parallel branches of the engine's air intake system to provide increased boost to the engine. One issue with twin turbocharged engines is that the amount of airflow provided by each of the turbochargers may become unbalanced. For example, degradation or failure of a turbocharger or other component of the exhaust system or variations in engine system components may cause one of the turbochargers to provide a larger portion of the total airflow to the engine than the other turbocharger. Thus, under these conditions, the engine system may generate noise and vibration harshness (NVH), experience reduced fuel efficiency, and/or the lower airflow turbocharger may experience compressor surge and may be damaged due to the imbalance of airflow provided by each turbocharger.
Some approaches aimed at addressing this issue have utilized a mass airflow sensor in each branch of the air intake system to reduce airflow imbalances resulting from imbalances in turbocharger operation. However, the inventors of the present application have identified some further issues with this approach. Specifically, the use of and reliance on separate mass airflow sensors in each air intake branch can add cost and complexity to the engine system. Further, failure or degradation of one of the mass airflow sensors can impair the ability to balance the airflow through each branch of the air intake passage.
As one example, the above issues may be addressed by a method of operating an engine system including a first air intake passage branch including a first compression device and a second air intake passage branch including a second compression device, wherein each of the first branch and the second branch are fluidly coupled to at least a combustion chamber the engine via a common intake passage, a first sensor arranged along the first branch and at least a second sensor arranged along the common intake passage, wherein the first sensor is a mass airflow sensor and wherein the second branch does not include a mass airflow sensor, the method, comprising increasing the mass airflow through the first branch relative to the mass airflow through the second branch when an amount of decrease in the mass airflow through the first branch is more than half an amount of a corresponding decrease in the combined mass airflow.
Thus, the combination of sensor outputs from a mass airflow sensor of only one of the two branches and an output from one or more sensors arranged in a combined flow region of the intake system can be used to identify imbalance between the two branches. In this way, an imbalance in mass airflow between two branches of an engine intake system, which may be caused, for example, by variations in compressor speed, can be reduced by the engine controller, while eliminating the need for a second mass airflow sensor in each branch of the air intake system.